Xerography is one type of an electrostatographic marking process. In this process, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image in a Xerographic system is generally developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The charged toner being electrostatically attracted to the latent electrostatic image areas to create a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material such as paper and the toner image is fixed thereto to form a permanent record corresponding to the original.
In a typical Xerographic monochrome copier or printer, a photoconductor surface is generally arranged to move in an endless path through the various processing stations of the Xerographic process. When the photoreceptor surface is reusable, the toner image is then transferred to a final support material, such as paper, and the surface of the photoreceptor is prepared to be used once again for the reproduction of a copy of an original. Although a preponderance of the toner image is transferred to the paper during the transfer operation, some of the toner and toner agents forming the image are unavoidably left behind on the photoconductor surface including residual wrong sign toner and toner additives. These remaining wrong sign toner and toner agents on the photoreceptor surface after the image transfer are referred to as residual toner and residual additives or agents. Residual toner also includes any patches or bands of right sign toner not transferred to the final support material. Many typical copiers or printers use particularly placed and developed patches or bands of toner for process control, and these patches or bands of toner must also be removed by the toner removal apparatus. Thus, substantially all residual toner and agents must be removed from the photoreceptor to prevent degrading or ghosting on subsequent copies reproduced by the copier or printer. Optimally, the residual toner and agents are removed without re-depositing the toner into the developer sump or onto the photoreceptor or smearing the toner on the photoreceptor surface as an unacceptable film.
One widely accepted method of cleaning residual toner from the surface of a photoreceptor of a typical copier or printer is by means of a cylindrical brush or brushes rotated in contact with the photoreceptor surface at a relatively high rate of speed. Generally, rotatable brushes are mounted in interference contact to the photoreceptor surface to be cleaned, and the brushes are rotated so that the brush fibers continually wipe across the photoreceptor. Electrical bias applied to conductive brush fibers aids in removing and transporting cleaned material away from the photoreceptor surface. In order to reduce the dirt level within the brush, a flicker bar and vacuum system may be provided which removes some residual toner and toner agents from the brush fibers and exhausts some of the residual toner and toner agents from the cleaner. Unfortunately, the brush could become contaminated with toner and toner agents and, after extended usage, needs to be replaced. Brush life is ultimately compromised by toner and additive impaction on fiber ends affects conductivity and physical changes to brush through mechanical or electrical breakdown that affect the mechanical integrity and/or electrical conductivity. With increased processing speeds of copiers and printers and the expanded use of toner agents, the foregoing brush cleaning techniques are not practical without substantial improvements.
Toner charge tends to drop in moist environments. Wrong sign toners can be created which contribute to broad charge distributions and resultant background on prints or image graininess. DualElectroStatic Brush cleaners have managed this issue in the past but have fallen from favor due to cost and process waterfront impacts. Charge distribution can be driven towards correct sign and pushed to higher Q/m, Q/d through changes in base resin, additives or carrier selection. However, these high-charging materials packages typically constrain development latitude in dry environments, eventually causing light prints or process controls faults or excessive toner concentrations or breakdown, etc. Also, in today's marking systems, toners are customized to contain certain toner agents to improve charge control toner transfer, flow and other desirable variations in the toner. Some agents include TiO2, SiO2, Zinc stearates and other known toner agents. There have been substantial ghosting and filming problems in these systems due to accumulation of wrong sign toners and these toner additives on the photoreceptor. While most prior art cleaning stations and electrostatic brush cleaners have been concerned with only right sign toner removal, it has become apparent that new and improved cleaning systems are needed for one brush to remove both wrong sign toner and toner agents or additives from the photoreceptor. Many difficulties were encountered to accomplish this primarily because of the very small size and relatively high amount of wrong charge of the toner and additives or agents. This has been further complicated because, for a functional solution, the wrong sign toner and additive cleaning latitude must sufficiently overlap the toner particle cleaning latitude. In addition, the removal of these wrong sign toner and toner agents becomes further complicated since the agents can be about 100 times smaller than the toner particle. While these agents are a dust size, they are highly charged and easily cling to the surface of the photoreceptor. Efficient removal of right sign toners and of these wrong sign toner agents and wrong sign toner is necessary to prevent or minimize ghosting and background on the final copy paper surface produced by the marking system or apparatus. It is recognized that while wrong sign toners may pass by a toner cleaning station, they have a propensity to be re-ingested by contact method development stations which are oppositely charged. This scavenging of wrong sign toner contributes, over time, to lowering the developer sump charge distribution.
Since most toners used today are negatively charged, the embodiments throughout this disclosure and claims will be described relating to the use of a negative toner. However, when a positive toner is used, the proper opposite adjustments can easily be made. Thus, when “wrong sign” toner or toner additives are referred to in this disclosure, the indication is that “wrong sign” designates a positively charged toner or additive. Therefore, “wrong sign toner” as used herein will include both wrong sign toner and wrong sign toner additives.